The main objective of this project is to increase our understanding of mechanisms involved in the metabolism of porphyrins in normal and disease states. Previous studies have shown that in porphyria cutanea tarda (PCT), a disease characterized by excess hepatic porphyrin synthesis, hepatic delta-aminolevulinic acid (ALA) synthase activity is not elevated. We propose to determine the significance of a pathway we have studied in mammals for the synthesis of ALA that differs from the usual condensation of glycine and succinyl-CoA. This novel pathway involves the transamination of the 5-carbon compound gamma, delta-dioxovalerate (DOVA) to yield ALA. We plan to study the synthesis of ALA from DOVA in hepatic and erythroid tissue in normal and porphyric animals and humans. The enzymatic decarboxylation of uroporphyrinogen is defective in patients with PCT and evidence suggests that multiple enzymes may be required for this 4 step reaction. With purified preparations of uroporphyrinogen decarboxylase (URODECARB) we plan kinetic studies using partially decarboxylated porphyrinogens as substrates to evaluate the hypothesis that at least two URODECARB enzymes exist. In association with these studies we plan to look for a multi-enzyme complex consisting of uroporphyrinogen I synthase, uroporphyrinogen III cosynthase and URODECARB which might have a regulatory function in heme biosynthesis. Finally we intend to study the incorporation of (13C) ALA and (13C) DOVA into porphyrins in vivo in patients with PCT and their relatives.